Vijay P. Singh

Aspects of Intramolecularly Coordinated Organochalcogen Derivatives

Recent progress in the area of intramolecularly coordinated organochalcogens, in particular, organoselenium derivatives, is reviewed. Intramolecular coordination facilitates isolation of (a) stable organoselenenyl iodides, (b) chiral diselenides, (c) organotriselenides, d) cleavage of Te─C bond, e) metal-free synthesis of chalcogenaaza macrocycles, and f) isolation of cyclic selenenate esters. The synthesis of organoselenium compounds incorporating two ortho-coordinating groups is also discussed.

Synthesis of novel heterocycles containing Se-O/Se-N linkages: Role of intramolecular coordination

The contrasting structure and reactivity of the mono ortho-coordinated aryl-and alkyl-selenium derivatives and 2,6-dibsubstituted aryl- and alkyl-selenium derivatives are described. The 2,6-disubstituted diaryl diselenides with Se ··· O intramolecular coordination and steric congestion around selenium undergo intramolecular cyclization to give the corresponding Se-O/Se-N heterocycles. The aliphatic analogue, 2-chlorocyclohex-1-ene-1,3-dicarbaldehyde (13), undergoes intramolecu- lar cyclization upon reaction with disodium diselenide to form a resonance stabilized cyclic diselenide (15). However, 2-chlorocyclohex-1-enecarbaldehyde (16), with one coordinating formyl group, does not undergo an intramolecular cyclization under similar reaction conditions. Diselenides, 2,2 � -bis(5-tert-butyl-benzene-1,3-dimethanol)diselenide (22) and bis(5-tert- butyl-isophthaladehyde) diselenide (23), with cissoid conformations are orange in color and show absorbances at longer wavelengths (368 and 380 nm respectively, n →*). The diselenides, bis(5-tert-butyl-isophthalic acid dimethyl ester)diselenide (24) and bis(5-tert-butyl-isophthalic acid diisopropyl ester)diselenide (25), with transoid conformations, are pale yellow in color with absorbances at shorter wavelengths (324 and 323 nm respectively, n →*). The intramolecularly stabilized arylselenenyl bromides with 2,6-disubstitution underwent interesting cyclization reactions to afford novel cyclic selenenate esters (with Se-O bond) and selenenamides and benzisoselenazoline (with Se-N bond) derivatives depending upon the ortho functions.

2-Bromo-3-nitro­benzaldehyde

The title compound, C7H4BrNO3, was isolated as a by-product while attempting to prepare a diselenide. There is a close intramolecular Br⋯O contact [2.984 (2) Å]. The molecules form loosely associated dimers held together by weak intermolecular Br⋯O interactions with the nitro O atoms [Br⋯O = 3.179 (3) Å]. As a result of these interactions, there is also a close Br⋯Br intermolecular contact [3.8714 (6) Å]. In addition, there are weak intermolecular C—H⋯O interactions. The combination of these interactions produces sheets which propagate in the (210) and (10) directions perpendicular to c.

Energy Efficient and Size Tunable Synthesis of ‘Colloidal’ Zinc Oxide Nanoparticles by Simple Beaker Chemistry

A facile approach to synthesize ‘colloidal’ ZnO nanoparticles with control over the size is presented here. All the synthesis was carried out at room temperature and simple beaker chemistry was utilized. The approach leads to slow growth of colloidal nanoparticles with saving of energy because no heating (room temperature) is required during reaction. To verify the nucleation and growth of the nanoparticles, time dependent UV–Vis absorption spectroscopy has been studied and found that growth of nanoparticles start within minute. Transmission electron microscopy and UV‐Vis absorption spectroscopy concludes that as reaction time increases particle size get larger and varies from 3–20 nm for 1 hour reaction time to 6 hour reaction time. XRD pattern of the ZnO nanoparticles shows a wurtzite crystalline nature which is supported by selected area electron diffraction measurement (SEAD), SEAD also confirms the polycrystalline nature of the ZnO nanoparticles. Photoluminescence of the colloidal solution of the ZnO...

Crystal structure of 4-bromo-N-(2-bromo-3-nitro­benz­yl)-2-nitro­naphthalen-1-amine

In the title compound, C17H11Br2N3O4, the dihedral angle between the planes of the naphthalene system and the benzene ring is 52.86 (8)°. The nitro substituent and the attached naphthalene system are almost coplanar [dihedral angle = 5.6 (4)°], probably as a consequence of an intramolecular N—H⋯O hydrogen bond with the amine group. The nitro substituent attached to the benzene ring is disordered over two sets of sites with occupancies of 0.694 (3) and 0.306 (3). The major component deviates significantly from the ring plane [dihedral angle = 53.6 (2)°]. In the crystal, the molecules are linked into a three-dimensional array by extensive π–π interactions involving both the naphthalene and benzene rings [range of centroid–centroid distances = 3.5295 (16)–3.9629 (18) Å] and C—H⋯O interactions involving the methylene H atoms and the phenyl-attached nitro group.